A conventional continuously variable transmission is a kind of automatic transmission and comprises pulleys, which are mounted to an input shaft and an output shaft and are provided with respective side plates having variable widths, and a power transmission belt comprising a steel belt and metal blocks. When each side plate of the pulleys is tapered and each pulley is configured as a wide pulley such that the power transmission belt is moved towards the center of the axles of the pulleys, the continuously variable transmission accomplishes operational effects expected by reducing the diameters of gears and reducing the number of teeth of the gears. Thus, the transmission can execute the speed change operation by controlling the widths of the pulleys using hydraulic pressure. The power transmission belt is constructed by setting the metal blocks in the steel belt such that power is transmitted in one direction determined by leaning motion of the metal blocks in the same manner as domino pieces which sequentially fall down.
In the conventional continuously variable transmission, the widths of the pulleys are changed by hydraulic pressure. When the input pulley is wider than the output pulley, the transmission changes the speed to a low speed. However, when the input pulley is narrower than the output pulley, the transmission changes the speed to a high speed.
However, the conventional continuously variable transmission causes severe friction between the power transmission belt and the pulleys, thus reducing its speed changing efficiency and its expected life span. Furthermore, the conventional continuously variable transmission executes the speed change operation by adjusting the widths of the pulleys, thus precise control of the operation thereof is not easy.